Evaporative Emission Control System

Fuel vapors trapped in the sealed fuel tank are vented through the fuel vapor valve assembly in the top of the tank, or vent cut valve at the fuel tank filler tube. The vapors leave the valve assembly through a single vapor line and continue to the carbon canister for storage until they are purged to the engine for burning.

Purging the carbon canister removes the fuel vapor stored in the carbon canister. The fuel vapor is purged via a purge control solenoid or vacuum controlled purge valve. Purging occurs when the engine is at normal operating temperature and off idle.

Fig. Fig. 3: Evaporative canister and hose routing on the 4.0L engine for 1994-97 B Series Pick-up and Navajo models

Fig. Fig. 4: Evaporative canister and hose routing for all 1998 B Series Pick-up engines-note location of the canister purge control solenoid

Fig. Fig. 5: Evaporative canister location-1994-95 MPV models

Fig. Fig. 6: Evaporative canister assembly-1996-98 MPV models

The fuel vapor canister is also referred to as evaporative emissions canister or charcoal canister.

The fuel vapors from the fuel tank are stored in the fuel vapor canister until the vehicle is operated, at which time, the vapors will purge from the canister into the engine for consumption. The fuel vapor canister contains activated carbon, which absorbs the fuel vapor. The fuel vapor canister can be found in the following locations:

1994-95 MPV-right side rear of the engine compartment

1996-98 MPV-underneath the right side of the vehicle toward the front

1994-97 B Series Pick-up and Navajo-left side radiator support, under the hood

This component is also known as the evaporative emission valve on 1995-98 models.

Fuel vapor in the fuel tank is vented to the carbon canister through the vapor valve assembly. The valve is mounted in a rubber grommet at a central location in the upper surface of the fuel tank. A vapor space between the fuel level and the tank upper surface is combined with a small orifice and float shut-off valve in the vapor valve assembly to prevent liquid fuel from passing to the carbon canister. The vapor space also allows for thermal expansion of the fuel.

Fuel Separator (MPV)

See Figure 7

Fig. Fig. 7: Fuel separator and cut valve assembly

The fuel separator is the component that prevents fuel from flowing into the fuel vapor canister. The fuel separator is located on the right side rear wheelhouse behind the interior trim panel. The fuel separator is not serviceable and should be checked periodically for damage or leaking. Replace the separator if damage or leaking is evident.

Cut Valve (MPV)

See Figure 7

The cut valve was previously referred to as the check & cut valve on 1994-95 MPV models.

The cut valve is mounted on top of the fuel separator, which is located on the right side rear wheelhouse behind the interior trim panel. The cut valve when necessary, releases excessive pressure or vacuum in the fuel tank to the atmosphere.

Check Valve (MPV)

See Figure 8

Fig. Fig. 8: Check valve location on 1996-98 MPV models

The check valve is also referred to as the two-way check valve.

On 1994-95 MPV models, the (two-way) check valve is mounted on top of the fuel separator, which is located on the right side rear wheelhouse behind the interior trim panel. On 1996-98 MPV models, the check valve is located on the right side of the engine compartment near the firewall. The check valve is used to control pressure in the fuel tank.

The canister purge control solenoid is inline with the carbon canister and controls the flow of fuel vapors out of the canister. It is normally closed. When the engine is shut
OFF
, the vapors from the fuel tank flow into the canister. After the engine is started, the solenoid is engaged and opens, purging the vapors into the engine. With the solenoid open, vapors from the fuel tank are routed directly into the engine. The canister purge control solenoid can be found in the following locations:

1994-95 MPV-right side front of the engine compartment next to the radiator

1996-98 MPV-right side of the engine compartment against the firewall

1994-97 B Series Pick-up and Navajo-left side radiator support, under the hood

1998 B Series Pick-up-mounted on the fuel vapor canister

Pressure/Vacuum Relief Fuel Tank Filler Cap

The fuel cap contains an integral pressure and vacuum relief valve. The vacuum valve acts to allow air into the fuel tank to replace the fuel as it is used, while preventing vapors from escaping the tank through the atmosphere. The vacuum relief valve opens after a vacuum of approximately-0.25 psi (1.7 kPa). The pressure valve acts as a backup pressure relief valve in the event the normal venting system is overcome by excessive generation of internal pressure or restriction of the normal venting system. The pressure relief is approximately 2 psi (14 kPa). Fill cap damage or contamination that stops the pressure vacuum valve from working may result in deformation of the fuel tank.

COMPONENT TESTING

Fuel Vapor Canister

See Figures 1, 2, 3, 4, 5 and 6

The fuel vapor canister is also referred to as evaporative emissions canister or charcoal canister.

Generally, the only testing done to the vapor canister is a visual inspection. Look the canister over and replace it with a new one if there is any evidence of cracks or other damage.

Do not try to check the fuel saturation of the canister by weighing it or by the intensity of the fuel odor from the canister. These methods are unreliable and inhaling gasoline fumes can be toxic.

Cut Valve (MPV)

The cut valve was previously referred to as the check & cut valve on 1994-95 MPV models.

1994-95 MODELS

See Figure 10

Fig. Fig. 10: Testing the cut valve using a vacuum gauge

Remove the cut valve from the vehicle.

Hold the valve in the horizontal position, otherwise the weight of the valve will cause it to move out of position and close the passage.

Connect a vacuum gauge in line to the passage which normally connects to the fuel tank - port
A
.

Blow air into port
A
and verify that the valve opens at a pressure of 0.79-0.99 psi (5.40-6.86kpa).

Remove the vacuum gauge and connect it to the passage to atmosphere- port
B
.

Blow air into port
B
and verify that the valve opens at a pressure of 0.15-0.71 psi (0.99-4.91kpa).

If not as specified, replace the valve.

1996-98 MODELS

See Figure 11

Fig. Fig. 11: Location of cut valve vacuum port A

Remove the cut valve from the vehicle.

While holding the valve in the horizontal position, blow air into port
A
and verify that their is air flow through the valve.

Next, hold the valve in the tilted position and blow air through port
A
again.

Verify that air does not flow through the valve.

If not as specified, replace the cut valve.

Check Valve (MPV)

The check valve is also referred to as the two-way check valve.

1994-95 MODELS

See Figure 12

Fig. Fig. 12: Two-way check valve testing

Remove the check valve and blow air through port
A
and check that the air flows.

Blow air through the opposite side port (port
B
) and check that the air does not flow through the valve.

Replace the valve as required.

1996-98 MODELS

See Figure 13

Fig. Fig. 13: Vacuum port identification for testing the check valve

Remove the check valve and blow air through port
B
and check that the air flows smoothly through port
C
.

Blow air into port
C
and check that the air flows smoothly through port
A
.

Replace the valve as required.

Canister Purge Control Solenoid1994 NAVAJO AND B SERIES PICK-UP MODELS

Remove the canister purge control solenoid.

Using an external voltage source, apply 9-14 DC volts to the purge solenoid electrical terminals. Then, use a hand-held vacuum pump and apply 16 in. Hg (53 kPa) vacuum to the manifold side nipple of the solenoid.

If the solenoid opens and allows air to freely pass through it, the solenoid is working properly.

If the solenoid does not allow air to pass freely while energized, replace the solenoid with a new one.

1995-98 B SERIES PICK-UP MODELS

Remove the canister purge control solenoid.

Measure the resistance between the two solenoid terminals.

If the resistance is between 30-90 ohms, proceed to the Step 3.

If the resistance is not between 30-90 ohms, replace the solenoid.

Attach a hand-held vacuum pump to the intake manifold vacuum side of the purge solenoid, then apply 16 in. Hg (53 kPa) of vacuum to the solenoid.

If the solenoid will not hold vacuum for at least 20 seconds replace it with a new one.

If the solenoid holds vacuum, proceed to Step 4. Keep the vacuum applied to the solenoid.